ICs comprise a collection of components such as transistors and resistors fabricated on a semiconductor substrate and connected together with conductive interconnections (e.g., metal, polysilicon, or including one or more other materials). Such interconnects can be referred to as “nets.” A combination of components and nets can form a system such as a microprocessor. In a digital or mixed-mode IC, small groups of transistors or other components form a gate or other element that can implement a logic function. Such a gate, or a group of gates can be referred to as a “cell.”
Cells may be standardized and selected from a cell library, allowing re-use of various logic functions across a design or between designs. Examples of cells can include inverters, OR gates, AND gates, exclusive OR (XOR) gates, NOT AND (NAND) gates, multiplexers, registers such as latches or flip-flops, adders, memories, or other more complex functions, such as including a combination of simpler elements structured in a hierarchical fashion. The logical arrangement of gates interconnected by nets can be used to synthesize a physical design comprising cells interconnected by physical nets. Such a physical design can then be fabricated on a semiconductor substrate to provide a functional IC.
Performance of the IC depends on its arrangement of cells and nets. The IC is designed by software packages called electronic design automation (EDA) tools that can be used to physically design or arrange cells, either using semi-automated physical layout, or in an automated fashion such as using one or more of a schematic design or a hardware description language. Such a design can then be simulated and modified in an iterative manner. In order to avoid costly design revisions, simulation such as formal verification can be used to verify that various representations of the design are equivalent.